The present invention relates to an air filter comprising a housing with an unfiltered air inlet and a filtered air outlet, and a round filter element sealingly disposed in the housing between the unfiltered air inlet and the filtered air outlet.
An essential development goal in modern internal combustion engines is to reduce emission of harmful substances. Until now, the development activities have focused primarily on optimizing the exhaust emission control system. Modern exhaust emission control systems meanwhile achieve conversion rates for harmful substances greater than 97%.
Increasing air pollution has led most countries to limit emissions and to continue to tighten these limits. To assure reproducibility and comparability, various test methods, ratings and limits have been developed. In the United States, for example, the limits include the categories ULEV (Ultra Low Emission Vehicle), SULEV (Super Ultra Low Emission Vehicle) and the current strictest category, PZEV (Partial Zero Emission Vehicle).
In connection with the above-described SULEV/ULEV problem, the disadvantage, however, is that hydrocarbons present in the intake manifold of an internal combustion engine, for example, may escape into the environment when the engine is stopped. Any occurring hydrocarbon emissions may have to be minimized in order to comply with the limits specified by law. It is also desirable to remove unburned hydrocarbons from the air guided into the passenger compartment of motor vehicles.
To solve this problem, components with adsorbent-containing filter elements are used in air circuits and air filter housings. Typically, the air ducts are made of plastic. The filter elements used are intended to reduce hydrocarbon emissions and/or prevent hydrocarbon emissions from being discharged. The filter elements are usually designed as pleated filters, ceramic-based solid structures, adsorbent-containing pressed materials or adsorbent beds. As a result, they require a special housing adapted for a given filter type and must be linked to the air circuits in an additional production or packaging step. The conventional filter elements, such as zigzag-shaped pleated filters are usually designed as replaceable cartridge filters.
Published U.S. patent application no. US 2003/082824 A1 discloses an air duct with integrated hydrocarbon sensor and collector. This device is disk-shaped and is situated inline in the air stream passing through the air duct. The adsorber element has a honeycomb structure and is preferably made of activated carbon or activated carbon and a binder.
Drawbacks in all of these solutions include their substantial production complexity, the considerable partial pressure loss and the required special adaptation of the housings and air ducts to the adsorber elements. A further problem is the need for desorbing the adsorber elements, which is typically done while the internal combustion engine is running. In an adsorber element in which the air flows through the element, the pressure loss is quite high but the desorption rate is good. In an adsorber element in which the air sweeps over the element, the desorption rate may be inadequate.